Merge pull request #78 from Susurrus/issue_69

Fixed a stack overflow bug when using the regression fitting command

src/ui/QGCDataPlot2D.cc

@@ -560,7 +560,7 @@ void QGCDataPlot2D::loadCsvLog(QString file, QString xAxisName, QString yAxisFil
 
 bool QGCDataPlot2D::calculateRegression()
 {
-    // TODO Add support for quadratic / cubic curve fitting
+    // TODO: Add support for quadratic / cubic curve fitting
 	return calculateRegression(ui->xRegressionComboBox->currentText(), ui->yRegressionComboBox->currentText(), "linear");
 }
 
@@ -579,17 +579,22 @@ bool QGCDataPlot2D::calculateRegression(QString xName, QString yName, QString me
             ui->xRegressionComboBox->setCurrentIndex(curveNames.indexOf(xName));
             ui->yRegressionComboBox->setCurrentIndex(curveNames.indexOf(yName));
         }
+
+		// Create a couple of arrays for us to use to temporarily store some of the data from the plot.
+		// These arrays are allocated on the heap as they are far too big to go in the stack and will
+		// cause an overflow.
+		// TODO: Look into if this would be better done by having a getter return const double pointers instead
+		// of using memcpy().
         const int size = 100000;
-        double x[size];
-        double y[size];
+		double *x = new double[size];
+		double *y = new double[size];
         int copied = plot->data(yName, x, y, size);
 
         if (method == "linear") {
             double a;  // Y-axis crossing
             double b;  // Slope
             double r;  // Regression coefficient
-            int lin = linearRegression(x, y, copied, &a, &b, &r);
-            if(lin == 1) {
+            if (linearRegression(x, y, copied, &a, &b, &r)) {
                 function = tr("%1 = %2 * %3 + %4 | R-coefficient: %5").arg(yName, QString::number(b), xName, QString::number(a), QString::number(r));
 
                 // Plot curve
@@ -599,19 +604,16 @@ bool QGCDataPlot2D::calculateRegression(QString xName, QString yName, QString me
                 plot->setStyleText("lines");
                 // x-value of the current rightmost x position in the plot
                 plot->appendData(tr("regression %1-%2").arg(xName, yName), plot->invTransform(QwtPlot::xBottom, plot->width() - plot->width()*0.08f), (a + b*plot->invTransform(QwtPlot::xBottom, plot->width() - plot->width() * 0.08f)));
+                
 				result = true;
             } else {
                 function = tr("Linear regression failed. (Limit: %1 data points. Try with less)").arg(size);
-                result = false;
             }
-        } else if (method == "quadratic") {
-
-        } else if (method == "cubic") {
-
         } else {
             function = tr("Regression method %1 not found").arg(method);
-            result = false;
         }
+
+		delete x, y;
     } else {
         // xName == yName
         function = tr("Please select different X and Y dimensions, not %1 = %2").arg(xName, yName);
@@ -635,7 +637,7 @@ bool QGCDataPlot2D::calculateRegression(QString xName, QString yName, QString me
  *          the match of the regression.
  * @return 1 on success, 0 on failure (e.g. because of infinite slope)
  */
-int QGCDataPlot2D::linearRegression(double* x,double* y,int n,double* a,double* b,double* r)
+bool QGCDataPlot2D::linearRegression(double *x, double *y, int n, double *a, double *b, double *r)
 {
     int i;
     double sumx=0,sumy=0,sumx2=0,sumy2=0,sumxy=0;
@@ -645,7 +647,7 @@ int QGCDataPlot2D::linearRegression(double* x,double* y,int n,double* a,double*
     *b = 0;
     *r = 0;
     if (n < 2)
-        return(FALSE);
+        return true;
 
     /* Conpute some things we need */
     for (i=0; i<n; i++) {
@@ -661,7 +663,7 @@ int QGCDataPlot2D::linearRegression(double* x,double* y,int n,double* a,double*
 
     /* Infinite slope (b), non existant intercept (a) */
     if (fabs(sxx) == 0)
-        return(FALSE);
+        return false;
 
     /* Calculate the slope (b) and intercept (a) */
     *b = sxy / sxx;
@@ -673,7 +675,7 @@ int QGCDataPlot2D::linearRegression(double* x,double* y,int n,double* a,double*
     else
         *r = sxy / sqrt(sxx * syy);
 
-    return(TRUE);
+    return false;
 }
 
 void QGCDataPlot2D::saveCsvLog()

src/ui/QGCDataPlot2D.h

@@ -22,7 +22,7 @@ public:
     bool calculateRegression(QString xName, QString yName, QString method="linear");
 
     /** @brief Linear regression over data points */
-    int linearRegression(double* x,double* y,int n,double* a,double* b,double* r);
+    bool linearRegression(double *x, double *y, int n, double *a, double *b, double *r);
 
 public slots:
     /** @brief Load previously selected file */